Induced-draft device



Aug. 21, 1923. 1,465,683

L. PRAT INDUCED DRAFT DEVICE.

Filed June 5, 1920 2 S hee ts-Sheet 1 I 72 I k Aug. 21, 1923. r 1,465,683

. L.PRAT

INDUCED DRAFT DEVI GE Filed June 5, 1920 2 Sheets-She et 2 Patented Aug. 21 1923.

warren star ers earest c LOUIS PRAT, 0F PARIS, FRANCE.

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I Application filedliune 3,

T .0 (LE whom it may 001mm; 1 Be it known that I, LoUIs Paar, citizen of the Republic of France, residing at Paris, France, 146 Avenue des Champs Elysees, have invented certain new and useful Improvements in Induced-Draft Devices, of which the following is a specification.

My invention relates to an induced dr aft device of the type in which a fan draws a portion only of the flue gases from the foot of the chimney and discharges it through a nozzle projecting inside, the chimney, said nozzle operating as an ejector to carrylalong the remainder of the gases whichrise directly up the chimney. The object of my improvement is to enable an induced draft device of this type to always operate with maximum efiiciency though the r volume. of the fiue gases may vary, for instancewhen the combustion increases or diminishes in the furnace producing said gases. I

The fanemployed in such devices is usnally a centrifugal fan driven byQan asynchronous electric motor which is adaptedto run only at substantially constant speed. But, so far as I am aware, in cases co'ntem plated in my present invention, the only method used up tothe present to meetthe variations of volume of the combustion gases is to provide, inside'the chimney above the blowing nozzle, va damper adapted to restrict the gas passage when their volume decreases." It is well known however that, when the passage is thus restricted, the efficiency of a centrifugalfan is considerably reduced, because a centrifugal fan, run at a given speed, possesses a satisfactory efiiciency only for a given volume of gases delivered by it.

The present invention permits of dispensing with a damper while avoiding the loss of efficiency of the fan. According to the invention a plurality of centrifugal fans.

driven at a constant speed are provided, each to deliver to the chimney a substantially constant volume of gases, and the number of fans in operation is varied as the total volume of gases to be delivered varies. Each fan is provided with a separate blowing nozzle and the several nozzles are preferably arranged concentrically.

The accompanying drawings illustrate various embodiments of the invention in diagrammatic form. Figure 1 is a vertical section of a chimney stack provided with two fans having two concentric blowing nozzles,

1920. Serial m. 335,378.

and Figure 2 is a, cross-section on line I teases FEF'EQE; 7'

ofFigure 1; Figurev 3 is a. cross-sectionof a: chimney with four concentric" blowing ozzles'; Figure4 is a cross-section of a" chim;

ney with four nozzles, disposed aroundthe a central axis of the chimney and Figure '5 .is

a-vertical section through one of thefans,

shown diagrammatically in the preceding figures, illustrating also in elevation the electricmotor driving such fan. a

In Figuresil and 2'two fans indicated by h,' j are placediat the footof a bi conica1 chimney e, that 1s to say a chimney which is constricted at one part a and then-widened out again above at a. Each fan is prov1ded w1th an inlet p or 12 open to the chimney sofas to receive thecornbustion gases, and their blades 9, such as are shown in the detail sectional view of Figure. 5, open into the stationary discharge spiral such as '9} which terminates in a delivery pipe gfor fan It and i for fan j. These pipes terminate in concentric blowing nozzles abend 0d respectively, which open into the chimney substantially in the ,central axis of the latter. V,The'twofansrh, j may vbe of equal or of dissimilar capacity; They are-each mounted on ashaft such as; (Figure 5), driven individually by .ani electric motor for other suitable means. i

When the maximum volume sr'combus tion gases 1S" delivered from the-furnace the two fans h, j, are run simultaneOuSly they draw in each a portion of the gases through their inlets p, p and force it out through nozzles ab and cal. The sectional area given each nozzle is that which affords the best efficiency for the given volume of gases delivered by each fan. The portion of gases blown through ab'and 0d working as ejectors carry along the remainder of come bustion gases which ascend directly up the chimney as shown by arrow F in Fig. l.

Then the volume of the combustion gases diminishes, one of the fans is-stopped and loo the other one which is still running then i alone supplies gases to the circular central nozzle (lb-assuming the fan to be h'or to the annular orifice comprised between ab and ed in the'case of fan j. Thus whichever fan remains in operation, it continues delivering substantially the same volume of gases through the same size orifice" as for,- merly.

The method of working is the same in the device shown in Fi nre 3 in which four v V b V Figures 1 and 2. One or more fans are set in operation as the volume of combustion gases increases, and each fan always deliv-.

ers substantially a constant volume of gases.

The blowing nozzles 70, Z, m, n, can also be arranged contiguous to each other around the'central axis of the chimney, as shown in the diagrammatic cross section of Figure 4. .But the concentric arrangement is obviously preferable in order that the discharge fIOIIYQZtChIIQ-Il may act with maximum efficiency on the gases surrounding them; in the chimney. Y V

It Will be obvious to any one skilled in the art that the invention'as disclosed is not limited to forcing fiue gases through a chimney, but is applicable to any draft device in which any kind of gas is forcibly moved through a chimney. I claim 1. In an induced draft device for chimneys or the like, a plurality of fans, each adapted to deliver a substantially constant volume of fiuid nto the chimney, and a permanently open discharge nozzle of pre determined size for each fan, disposed in discharged by the fan to carry along the chimney gases-in ejector fashion.

3. In an induced draft device, a biconical chimney, a plurality of centrifugal fans each adapted to deliver a substantially constant volume of fluid into said chimney, the number of said fans in operation being proportional to the total Volume of combustion gases in the chimney, and a permanently open discharge nozzle of predetermined size for each fan, said nozzles' being disposed in the chimney'throat concentrically to each other and to the central axis ofthe chimney, said nozzles adaptedto cause the fluid dischargedfrom them to carry along the chimney gasesin ejector fashion;

a. In "an induced draft device for chimneys or the like, a plurality of fans each adapted to delivera substantially constant volume of fluid intothe chimney, and each adapted to operate independently of the others, and a permanently open discharge nozzle of predetermined size for each fan disposed in the chimney to cause the fluid discharged by the fan to carry along the chimney gases in ejector fashion, the number of fans operating at a given time be-, ing proportioned to the total volume of gases passing thru the chimney at that time.

5. In aninduced draft device for chimneys or the like, aplurality-of fans, each adapted to dravvfrom and return into the chimney a substantially. constant volume of combustion gases, and each fan adapted to operate independently of'the others, anda permanently open discharge nozzle of predetermined size for each fan and disposed in the chimney to cause the gases discharged by the fan to carry along the remainder V of'thechimney gases in ejector fashiong In testimony WhereofI aflixmy signature." LoUIs' Paar, if 

